Can a vaccine against a different microbe provide protection against SARS-CoV-2?

Nonspecific immune enhancement by BCG or MMR vaccines: Maybe, but I wait for data.

A few days ago, the American Society for Microbiology wrote a press release about an article in one of their journals. The headline: MMR Vaccine Could Protect Against the Worst Symptoms of COVID-19.

The operative word here is “could.” Actual data to support this assertion are totally lacking.

Here’s the backstory, and why this idea is scientifically plausible, if not experimentally justified:

First, you need to understand that any vaccine is designed to create specific immunity against a specific virus (or bacterium). That means a vaccine against polio does nothing to protect you from smallpox. Vaccines are designed to stimulate the parts of the immune system that recognize and attack specific targets (antigens). Often, this means vaccines cause your body to produce antibodies.

But the immune system is phenomenally complex, not just antibodies, and it includes a wide range of nonspecific responses too. Some vaccines also prime the immune system to better fight against infections in general. This effect is not huge but it can be real. The effect has been documented with the BCG vaccine. BCG is a not-particularly-effective vaccine against tuberculosis that in some situations has general immune boosting effects. Early in the coronavirus pandemic, people hoped that BCG might give some (nonspecific) protection against SARS-CoV-2. So far, the data have not supported this idea.

Now, back to the paper. The investigators posit that the MMR (measles, mumps, rubella) vaccine given to all children could have a nonspecific immune-boosting effect. They further argue that MMR boosters for adults might therefore provide some protection against the worst cases of COVID-19. Unfortunately, they do not provide data to directly support these assertions. Their only experimental work is in mice, and it’s not even with MMR. The paper looks to me like some scientists doing good work in a poorly funded niche, trying to sex it up by tying in with coronavirus.

Just because it makes sense doesn’t make it true

You can’t count the number of times in medical science when somebody had a really good idea, that was logical and fact-based, that had some evidence from a test tube experiment or an animal model—and turned out to be completely wrong when properly investigated in humans.

A well-designed clinical trial is the best—really, the only—tool we have to establish whether a treatment works. Anecdotes and theories are persuasive but totally unreliable.

Remember when Trump went all-in with his “good feeling” about hydroxychloroquine, the anti-malaria drug? He was pilloried for touting this unproven treatment, and rightly so, but this MMR report takes a similar approach (without the politics). About hydroxychloroquine Trump said, “We ought to give it a try,” because he believed there was no downside risk (which is not correct, the drug has potential negative effects). In this press release about the MMR vaccine, one of the investigators says, “While we are conducting the clinical trials, I don’t think it’s going to hurt anybody to have an MMR vaccine.”

While that may be true, I personally find this category of argument problematic. It might work, it doesn’t hurt to try. Sure, but where do you draw the line? Lots of things might work, and might not hurt to try. Should I try them all? At some point, it just might hurt to try, or at least be a waste of my time and money (see: virtually all food supplements). With the SARS-CoV-2 pandemic, because billions of people are at risk, urging people to try something unproven can cause unforeseen harm. For example with hydroxychloroquine, supply of the drug quickly was exhausted. This meant patients who relied on the drug for its known, intended therapeutic benefits had trouble getting their medicine. The same would likely happen if American adults en masse started getting MMR shots—the vaccine would run out, and children who need it to protect them from measles might not get it.

Hydroxychloroquine might have turned out to be effective against COVID-19. It did not. Trump’s error was to pick a winner without good clinical evidence, before proper studies were done. This MMR report strikes me as similar. Maybe it will be a breakthrough discovery. Maybe it won’t. I will wait for the trial data.

Dexamethasone

Speaking of trial data, did you hear the excellent news last week about dexamethasone? Honestly, this is some of the best news we’ve had in the fight against COVID-19. Why is it that solid scientific work like this doesn’t go viral the way conspiratorial nonsense does?

STAT News, one of my trusted sources, reports on pre-publication data from a study out of the UK that shows dexamethasone, a cheap, widely available, well-understood anti-inflammatory corticosteroid drug, cuts the death rate of ventilated COVID patients by 35%. That’s a huge number, a huge impact on the very sickest coronavirus patients. The data are consistent with our evolving understanding that an overactive immune response contributes to the disease. 

This is pre-publication data (“study results by press release”), not the best way or the normal way for medical science to proceed, so it’s possible the results will be retracted or modified later. But this was a large, randomized controlled trial performed by a respected clinical group, and the effect is so large, that there’s probably truth in it. I’m sure that in hospitals all over the world, treatment protocols continue to be improved.

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